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All of the content that you have on a subdomain and all of the links that the subdomain attracts could have been working to strengthen your root domain. In Google you are going out to fight the heavyweights.  Do you want to do that with a couple light weight platforms or do you want to unite the clans and attack with all that you got.   That is the choice that you make by running subdomains. I moved and redirected my subdomains into folders on the main website a long time ago and the results were great.